Morpho-anatomical and physiological traits of Agrostis castellana living in an active geothermal alteration field

Agrostis castellana is one of the few plants colonizing one of the most extreme geothermal alteration fields characterized by low pH and high temperature of soil.The study of species surviving in these multi-stress habitats can help to know more in deep the adaptive ability of plants. In this work morpho-anatomical, functional and physiological traits of leaves of A. castellana living few meters from fumaroles were studied, focusing on their putative ecological significance.Some typical xeromorphic traits occurred in the leaves of these plants: abundant cutinization, cell wall thickening, slightly convolute and adaxially ribbed leaf blades, tissutal reinforcements by sclereids, pubescence, protected stomata and densely packed mesophyll. Abundant pectins, important in both water balance adjusting and as monosaccharide source, were observed in epidermal cell walls. Despite the low value of relative water content, indicative of a disturbed hydric state, oxidative damage, in terms of lipid peroxidation, indicative of membrane damage, was significantly lower than in other plants of the same environment, probably tanks to an adequate antioxidant response based mainly on enzymatic machinery. Interestingly catalase activity was not inhibited by extreme conditions of the geothermal alteration field as in other plants of the same habitat. In conclusion, a cooperation of xeromorphic traits and antioxidant response seems to make A. castellana able to survive in such a prohibitive environment.

Occurrence of Ustilago striiformis in Dactylis glomerata Seed Production Fields in Oregon

Stripe smut, caused by Ustilago striiformis, is a common disease of grasses grown for turf, but quantitative information concerning its occurrence in grass seed production fields is lacking. In 2004, 2005, and 2006, stripe smut was detected in 16, 17, and 3 out of 51, 42, and 33 Dactylis glomerata (orchardgrass) seed production fields surveyed in western Oregon, respectively. Stripe smut was not previously known to occur in these fields. The percentage of plants per transect with stripe smut in 2004, 2005, and 2006 ranged from 0 to 12, 0 to 4, and 0 to 1, respectively. In additional surveys during 2004-2006, to determine whether stripe smut was also occurring in seed production fields of other grasses in western Oregon, stripe smut was found in one field of Agrostis stolonifera, but was not detected in fields of Agrostis castellana, A. capillaries, Festuca arundinacea, F. longifolia, F. ovina, F. rubra subsp. commutata, F. rubra subsp. rubra, or Lolium perenne. Accepted for publication 9 July 2007. Published 23 October 2007.

First Report of Choke Disease Caused by Epichloë baconii in the Grass Agrostis castellana

Agrostis castellana is common in semiarid natural grasslands of the province of Salamanca, Spain. In this area, plants showing fungal stromata in their stems were observed in July of 2001. These symptoms are typical of choke disease, caused by Epichloë species in several grasses (3). In this disease, external fungal stromata develop around the leaf sheath of the flag leaf during the reproductive cycle of the plant host. As a result, the inflorescence does not emerge. In natural populations of A. castellana, less than 1% of plants showed disease symptoms, and all the stems of infected plants were sterilized by stromata. Intercellular endophytic mycelium was observed by microscopy in stem pith of diseased plants, but not on samples of 30 apparently healthy plants (1). Ergovaline, a fungal alkaloid, was not detected in lyophilized samples of infected plant tissue (2). In a fungal culture obtained from surface-disinfected leaf sheaths of a diseased plant (1), reniform conidia and conidiophores characteristic of the genus Epichloë were observed (4). To determine the fungal species, the nucleotide sequence of the ITS1-5.8SrRNA-ITS2 region and the three first introns of the beta-tubulin gene were obtained (EMBL Accession Nos. AJ490938 and AJ490939). When compared to those of other Epichloë species, these sequences identified the fungus from A. castellana as E. baconii (3). This fungus has been previously described as a pathogenic fungal endophyte in other Agrostis and Calamagrostis species (3,4). The fact that all stems of infected plants were diseased, infection incidence was low, and no alkaloids were detected in plants suggests that this grass-endophyte interaction is pathogenic and not mixed or mutualistic. References: (1) E. Clark et al. J. Microbiol. Methods 1:149, 1983. (2) N. Hill et al. Crop Sci. 33:331, 1993. (3) A. Leuchtmann et al. Mycol. Res. 102:1169, 1998. (4) J. White Jr. Mycologia 85:444, 1993

Effect of pasture renovation on the size and composition of the germinable fraction of the seed pool beneath bent grass (Agrostis castellana) pastures in southern Victoria

This paper investigated the potential for propagation of grass weeds from seed by measuring changes in the size and composition of the germinable fraction of the seed pool beneath 4 bent grass (Agrostis castellana) pastures in southern Victoria during renovation. Soil samples, for the estimation of the seed pool by seedling emergence in the glasshouse, were taken from a control and a renovated pasture on 3 occasions during renovation at each of the 4 sites. The depth distribution of seeds in the top 0–100 mm was assessed by dividing collected soil samples into depths of 0–30 mm and 30–100 mm. The total germinable seed pool (0–30 mm) ranged from 17 620 to 83 540 seedlings/m2, as affected by the time of sampling. There were seedlings from 14 grass genera (12% contribution to the total seed pool), Juncus (60%), 4 leguminous genera (17%), and 22 other dicotyledonous genera (12%). The percentage change in the number of germinated seeds of grasses and dicotyledons between the first and second sampling was negative ( –7·3% to –31·4%) beneath renovated pasture, as opposed to a positive change (29·0–174·4%) beneath undisturbed pasture; this was attributed to the prevention of seeding due to the cultivation of the pasture associated with renovation. The percentage change in the number of germinated seeds of grasses and dicotyledons did not differ significantly between renovated and undisturbed pasture between the second and third sampling, which suggested that no more seed germinated in response to renovation. Re-distribution of germinable seed to lower depths (30–100 mm) with renovation was apparent for grasses and other dicotyledons, and would depress successful emergence of these seedlings. Renovation prevented re-seeding of weeds and buried surface seed, but did not significantly stimulate additional seed to germinate the following autumn after renovation. Weed seeds were still present in the soil seed pool after renovation, which indicated that these species could potentially germinate and establish in new pastures.

Length of rhizome and depth of burial affects the regeneration of bent grass (Agrostis castellana Boiss. et Reuter)

Renovation of pastures dominated by bent grass (Agrostis castellana), by killing the vegetation with herbicides followed by cultivation and re-sowing, according to current recommendations, can kill up to 95% of the bent grass. To improve the success of killing bent grass and reducing the likelihood of regeneration from rhizomes after renovation, the behaviour of rhizomes after fragmentation was studied in pots. Rhizomes were cut into different lengths (15, 40, and 100 mm) to contain 1, 3, and 8 nodes per section and planted at depths of 25, 50, 75, 100, and 200 mm in cultivated soil, with or without competition from establishing seedlings of perennial ryegrass and white clover. The proportion of bent grass shoots developing from buried rhizomes was reduced to <10% when rhizomes were broken into sections containing only a single node and buried at or below 75 mm. Even after 3 months burial, an average of 0, 0·2, and 0·4 nodes in 1-node, 3-node, and 8-node sections, respectively, were still viable after fragmentation and could potentially develop, should conditions change, ensuring regeneration. The presence of newly sown pasture did not affect either the development of nodes or the vigour of shoots of bent grass during the 3-month measurement period. Pasture production, however, was reduced with increasing bent grass shoot production such that 8-node sections buried at 25 and 50 mm produced up to 3 times more dry matter per pot than other pasture components, giving bent grass a competitive advantage.

Agrostis castellana (Poaceae), Dominant Agrostis Species, Found in Bent Grass Pastures in South-eastern Australia

There is considerable uncertainty that the traditional identification of bent grasses in south-eastern Australia as Agrostis capillaris L. (Syn. Agrostis tenuis Sibth.) is correct, due to a history of confusing nomenclature and mis-identification. Bent grass is considered a weed of pastures in the high-rainfall zone of south-eastern Australia and thus the correct identity of bent grass may have implications for its management and control. Populations of bent grass were sampled from 42 pastures in south-eastern Australia and Agrostis castellana Boiss. et Reuter, rather than A. capillaris, was found to be the dominant species of Agrostis in 33 out of 42 bent grass pastures sampled. Five of the nine pastures sampled in Tasmania contained A. capillaris as opposed to only 1 of the 33 pastures sampled in Victoria. Agrostis castellana had not been identified in Victoria or Tasmania prior to this work. Since A. castellana grows more vigorously by rhizomes than A. capillaris, control measures recommended for A. capillaris may not be relevant for bent grass pastures in south-eastern Australia. Ligule length, ligule width and width of lamina, measured to determine whether species of bent grass could be easily distinguished in the field, did not distinguish adequately between A. castellana and A. capillaris.

Use of glyphosate to prevent development of reproductive tillers and extend vegetative growth of bent grass (Agrostis castellana)

The effect of glyphosate on seedhead development of bent grass (Agrostis castellana) was evaluated in an experiment at 2 sites in south-western Victoria.Application of glyphosate at 0.1350.225 kg a.i./ha on 7 November and 7 December 1993 prevented the formation of seedheads and stimulated the plant into renewed vegetative growth in response to following summer rain. The treatment with 0.135 kg a.i./ha of glyphosate, applied on 7 November, increased digestible dry matter of the regrowth by 20% and protein content by 70% compared with the unsprayed control which was dominated by seedheads. These results reflect the amount of new growth in treated plots and thus should not be confused with either the 'spraytopping' technique which aims to sterilise seeds after seedhead emergence or 'hay freezing' which and aims to preserve the feed value of existing vegetation by 'chemically curing' standing hay. We conclude that application of glyphosate at 0.135 kg a.i./ha in early November has the potential to reduce the dominance of bent grass, creating an opportunity for follow up fertiliser and management techniques to maintain productive pastures.